United States

The United States of America (USA or U.S.A.), commonly known as the United States (US or U.S.) or America, is a country primarily located in North America, between Canada and Mexico. It is a liberal democracy and republic of 50 federated states, a federal capital district (Washington, D.C.), and 326 Indian reservations that overlap with state boundaries. Outside the union of states, it asserts sovereignty over five major unincorporated island territories and various uninhabited islands. The country has the world's third-largest land area, largest maritime exclusive economic zone, and the third-largest population (over 334 million). The federal government uses a presidential system with three separate branches: legislative, executive, and judicial.

American territory was first settled when Paleo-Indians migrated across the Bering land bridge more than 12,000 years ago. British colonization began in 1607. Thirteen colonies rebelled against the Crown over taxation and political representation, declaring independence on July 4, 1776. Their victory in the American Revolutionary War (1775–83) resulted in a confederation of states that went on to ratify the U.S. Constitution and Bill of Rights. The young nation began to acquire neighboring territories and spanned North America by the late 1840s. Longstanding disagreements over slavery led to the secession of the southern Confederate States of America, which were defeated by the remaining Union in the American Civil War (1861–65). Slavery was abolished, but discriminatory laws persisted in the South. By 1900, rapid industrialization established the United States as a great power and the world's largest economy. After the Japanese attack on Pearl Harbor in December 1941, the United States joined the Allies of World War II. Following their victory, it competed against the Soviet Union for dominance in arms, ideology, international influence, and space during the subsequent Cold War. Many racist practices in the country were overturned in the 1960s, and it became the first to land humans on the Moon (1969). The nation emerged as the world's sole superpower after the dissolution of the Soviet Union and the end of the Cold War (1991).

The United States accounts for about 25% of the global economy and 30% of global wealth. It has the largest nominal GDP and ranks among the highest in the world in measures of income, wealth, economic competitiveness, productivity, innovation, human rights, and higher education. The country is home to globally important industries in aerospace and defense, automobiles, energy, entertainment, finance, healthcare, and information technology. The United States is a founding member of the United Nations (UN), the North Atlantic Treaty Organization, the Organization of American States, the International Monetary Fund, the World Bank, the World Trade Organization, and is a permanent member of the UN Security Council.